(a) Field of the Invention
The invention relates to a rotor assembly and, more particularly, to a rotor assembly that contributes to the construction of a thin motor.
(b) Description of the Related Art
Nowadays, designers continually make an effort to reduce the size of the electrical product; for instance, the notebook gradually becomes thinner and thinner. Under the circumstance, a fan motor used for dissipating heat is designed to reduce its overall thickness when applied to the miniaturized electrical product.
A conventional design for reducing the size of a fan motor is shown in FIG. 1, where the rotor housing 104 is provided with a drive boss 104A under the hub 106, and a longitudinal notch parallel to the shaft 102 is formed. Thereby, the extended section 106A of a hub 106 can be placed in the longitudinal notch, thus providing a reduced hub diameter and further reducing the lateral width of the constructed motor structure.
However, the extended section 106A must be of such a length that it can hold a fan blade. The longitudinal notch, therefore, must be large enough to accommodate the downwardly extended section 106A, resulting in decreasing the space provided for the coil 108 and the permanent magnet 110 and thus limiting the fan motor 100 in the maximum output power.
Moreover, the hub 106 is usually made of materials with poor heat conduction such as plastic, once the top of the rotor housing 104 is fully covered with the hub 106 according to the conventional design, the hub 106 is liable to obstruct the heat-dissipation.